I have a SharePoint 2010 site using a custom themed master page. It does not show the standard SharePoint ribbon. However, users are able to append showRibbon=true to their URL to see the ribbon. I don't mind if users in the SP Administrators group do this but how can I prevent users in other groups from seeing and accessing the ribbon altogether.
You can use Sharepoint:SPSecurityTrimmedControl . Add the tags for ribbon inside this tag.It will be displayed to only those users who has the permission specified in the permission string.
<Sharepoint:SPSecurityTrimmedControl runat="server" PermissionsString="FullMask"> </Sharepoint:SPSecurityTrimmedControl>
Below is link ablout the permission string properties with allowed values: http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.webcontrols.spsecuritytrimmedcontrol.permissionsstring.aspx